[test] Make test filters platform-independent.

[test] Make test filters platform-independent.

Use the same path separator for test cases on the cmd-line
on all platforms as in testcase.GetLabel, which is used to
report failures.

BUG=chromium:511215
LOG=n
NOTRY=true

Committed: https://crrev.com/7ce3afa0df92cad3c1ecc6ff350250f97fbc9d70
Cr-Commit-Position: refs/heads/master@{#30045}

[Michael Achenbach, 2015-08-06 09:35:47]

machenbach@chromium.org changed reviewers:
+ jkummerow@chromium.org

[Michael Achenbach, 2015-08-06 09:37:47]

PTAL

[Jakob Kummerow, 2015-08-06 09:42:51]

LGTM!!!!!!!!!!!!!111eleven

[Michael Achenbach, 2015-08-06 12:34:54]

The CQ bit was checked by machenbach@chromium.org

[commit-bot: I haz the power, 2015-08-06 12:35:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1281453003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1281453003/1

[commit-bot: I haz the power, 2015-08-06 12:36:54]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-06 12:37:06]

Patchset 1 (id:??) landed as
https://crrev.com/7ce3afa0df92cad3c1ecc6ff350250f97fbc9d70
Cr-Commit-Position: refs/heads/master@{#30045}